This study will address the hypothesis that 3tc is uniquely effective in combination with zdv due to the interaction of zdv and 3tc resistance mutations. The antiviral activity of 3tc/zdv will be compared with that of 3rc/ddi and 3tc/4dt combinations, as well as with dii and d4t monotherapy in previously untreated subjects with cd4 count 200-600 cells/mm3. The relative antiviral activity of these regimens will be assessed by suppression of plasma HIV-1 RNA levels. Uncultured cells and plasma will be stored for assessment of rt genotype. Culture supernatants will also be saved as a source of virus stocks, and cells will be frozen at end of culture as dry pellets for possible future genotypic analysis. It is anticipated that 3tc resistance will emerge quickly, based on the results of previous studies. This study will enable us to examine the potential importance of cross-resistance between dd1 and 3tc conferred by the m184v mutation by comparing the activity of the 3tc/ddi combination with ddi monotherapy. In addition, interactions of 3 tc resistance with d4t will be studied by comparing the activity of 3tc/d4t with d4t monotherapy. The d4t monotherapy arms, since there are as yet no data available comparing zdv and d4t in previously untreated patients. The current study will examine the safety of these combinations. In addition, a pharmacologic substudy will be conducted to study possible pharmacokinetics interactions of the combinations.